int fibonacci(int n) {
  if (n == 0 || n == 1) return n;
  return fibonacci(n - 1) + fibonacci(n - 2);
}

String greet(String name) {
  return '你好，$name！';
}

void main() {
  print(greet('小可爱'));

  var result = fibonacci(20);
  print('斐波那契数列第20项是：$result');
}
